U.S. Pat. No. 3,523,957 A (The Lummus Comp., “Process for Producing an Olefinic Oxide”) relates generally to a process for producing olefin oxides.
DE 23 44 499 A (The Benfield Corp., “Waschlösung für saure Gase and ihre Verwendung” [Scrubbing solution for acid gases and use thereof]) and U.S. Pat. No. 3,907,969 A (The Benfield Corp., “Separation of CO2 from Gas Mixtures”) describe, as solvent for the CO2 absorption, a potash solution which is activated by inorganic salts.
The EP patent application having the application number 09159104.0 of Apr. 29, 2009 (BASF SE) relates to absorption media for removing acid gases from a fluid stream comprising an aqueous solution of cyclic amine compounds.
WO 03/022826 A1 (Scientific Design Comp., Inc.; “Heat Recovery Procedure”) describes a method for heat recovery in the discharge of CO2 in ethylene oxide production. In a special scrubbing column, the cycle gas is first heated, then passed to the potash CO2 absorber and thereafter the gas is cooled again (figure on page 9 of the WO publication). As heat carrier medium, water is used which is heated in the afterscrubber and gives off its heat again in the prescrubber. Advantages mentioned are the reduction of glycol formation in the potash CO2 absorber by reduction of ethylene oxide in the supplied cycle gas. In addition, the afterscrubber leads to the removal of water which is necessary for the reaction procedure, since water, according to the teaching of the patent application, is disadvantageous to the catalyst. Further advantages mentioned are the low pressure drop compared with thermal integration via heat exchangers.
Disadvantages: the special apparatus into which both scrubbers are integrated is very complex.
WO 03/082844 A1 (BASF AG, “Verfahren zur Herstellung von Ethylen oxid mit integrierter Kohlendioxidwäsche” [Process for producing ethylene oxide having integrated carbon dioxide scrubbing]) teaches a process for producing ethylene oxide from ethylene and O2 in which CO2 is ejected using an aqueous amine solution which comprises a tertiary alkanolamine and optionally an aliphatic secondary amine.
The patent application, for operating the CO2 removal, describes preferably a solvent which essentially comprises only the tertiary alkanolamine, in particular N-methyldiethanolamine (MDEA) and an aliphatic secondary amine, in particular PIP. According to the teaching of the patent application, the gas stream leaving the CO2 absorber can be brought into contact with an aqueous solution of a mineral acid or a higher glycol (page 6, 2nd paragraph).
Disadvantages: the glycol solutions or mineral acid solutions must subsequently be regenerated in a complex manner in order to remove the condensed water. The regeneration leads to an increased expenditure in terms of apparatus and increases the operating costs of the process. When the glycol solution is treated, in addition to the water, in addition, amines which are still dissolved must be removed in order to avoid accumulation. The amines have good solubility in glycol solutions. The amines which are commonly used in gas scrubbing in addition have a higher boiling temperature than water, and so the glycol solution must be distilled at high temperature or in a vacuum, which greatly increases the expenditure in terms of apparatus and the operating costs. Since in addition, amines can be formed by degradation which have a higher boiling temperature than the glycol solution, the distillation must be carried out in two separate apparatuses.
Furthermore, owing to the glycols, a new substance is introduced into the process which is associated with increased costs.
WO 01/98285 A1 (Eastman Chem. Comp., “Process for the removal of carbon dioxide from 3,4-epoxy-1-butene process recycle streams”) describes in particular for the production of 3,4-epoxy-1-butene (EpB) from butadiene and O2 a process for removing CO2 using an aqueous or alcoholic alkanolamine solution, wherein the alkanolamines are primary and/or secondary alkanolamines each having up to ten carbon atoms and having a respective boiling temperature of below 250° C. (page 15, line 27 to page 16, line 1).
Traces of amines (15 vol.-ppm) are described as being able to damage reversibly the silver-based catalyst (page 19, lines 25-27). In particular, the content of amines in the gas downstream of the CO2 scrubber must be reduced to less than 10 vol.-ppm, preferably 5 vol.-ppm, and particularly preferably 1 vol.-ppm. As a possibility for removing amines, a scrubbing column is mentioned. As scrubbing solvent, water is preferred (page 20).
A difference from the ethylene oxide production process is the fact that degradation products which form in the amine solution in the production of EpB are relatively long-chained, since butenols are concerned, whereas in the production of ethylene oxide, shorter-chain ethanols form. Therefore, other degradation products form and tertiary amines are not used in the absorption medium, therefore the gas phase which forms is also a different one. Application of the results from an EpB production process to an EO production process, in particular also with respect to the scrubbing action of a water scrubber, is therefore not possible.